In various topological phases, nontrivial states appear at the boundaries of the system. In this paper, we investigate anomalous dielectric response caused by such states caused by the π Zak phase. First, by using the one-dimensional Su-Schrieffer-Heeger model, we show that, when the system is insulating and the Zak phase is π , the polarization suddenly rises to a large value close to e/2, by application of an external electric field. The π Zak phase indicates the existence of half-filled edge states, and we attribute this phenomenon to charge transfer between the edge states at the two ends of the system. We extend this idea to two-and three-dimensional insulators with the π Zak phase over the Brillouin zone and find similar anomalous dielectric response. We also show that diamond and silicon slabs with (111) surfaces have the π Zak phase by ab initio calculations, and show that this anomalous response survives even surface reconstruction involving an odd number of original surface unit cells. Another material example with an anomalous dielectric response is polytetrafluoroethylene (PTFE), showing plateaus of polarization at ±e by ab initio calculation, in agreement with our theory.
A highly efficient nonlinear optical response in terms of both low threshold intensity and high stability is achieved in polymer‐stabilized liquid crystals doped with a small amount of oligothiophene. Polymer stabilization decreases the threshold intensity by a factor of 6, and a large refractive index change of 0.14 is stably maintained up to high (>110 W cm‐2) pump intensities.
Nonlinear optics deals with phenomena where “light controls light”; e.g., there is mediation by an intensity-dependent medium through which light propagates. This field has attracted much attention for its immense potential in applications dependent on nonlinear processes, such as frequency conversion, multiple-photon absorption, self-phase modulation, and so on. However, such nonlinearities are typically only observed at very high light intensities and thus they require costly lasers. Here, we report on a self-focusing effect induced with a 1 mW handheld laser pointer. We prepared polymer-stabilized dye-doped liquid crystals, in which the molecular director orientation gradually changes from homeotropic at one surface to homogeneous at the other. This is referred to as hybrid alignment. In such films, the threshold intensity needed to form diffraction rings was reduced by a factor of 8.5 compared to that in conventional homeotropic cells, which enabled the induction of the self-focusing effect with a laser pointer.
Lithium intoxication infrequently results in symptoms that closely resemble those of Creutzfeldt-Jakob disease (CJD), that is accompanied by periodic sharp waves on EEG. We present the case of a 77-year-old female patient with lithium intoxication and a rapid-onset coma and showing few abnormal neurological fi ndings and periodic sharp waves on EEG. As far as we have surveyed, there have been no reported cases of lithium intoxication in which periodic sharp waves appeared without symptoms mimicking those of CJD. This is the fi rst case in which periodic sharp waves appeared without lithium-induced symptoms mimicking those of CJD, and this case emphasizes the need to monitor the EEG fi ndings during lithium therapy.
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